1. Field of the Invention
This invention relates to vehicle braking systems. More specifically, this invention relates to a fluid distribution control system for use with a closed system application of an anti-locking braking system.
2. Description of the Prior Art
Presently, some closed antilocking brake systems (ABS's) operate in three basic modes or phases. First, a pressure increase mode is initiated when a vehicle operator applies pressure to a brake pedal in order to initiate a braking action. The ABS operates in pressure increase mode while it is desirable to increase the pressure within the system thereby increasing the pressure that the brakes exert against the wheels to cause deceleration of the vehicle. When the pressure within the system becomes so great as to cause the wheels to "lock" in an undesirable fashion, the ABS enters a pressure hold mode. During the pressure hold mode, a constant pressure is maintained within the brake conduits of the system to provide continued deceleration of the vehicle while concomitantly preventing undesirable wheel lock. A third mode, which typically follows the pressure hold mode, is known as the pressure decrease mode. The pressure decrease mode is typically used when no further pressure is desired for forcing the brakes against the wheels or where a decreased pressure within the brake network is desirable. The pressure decrease mode includes dumping or removing the brake fluid from the brake network conduits and returning it to the master cylinder. During pressure decrease, the fluid first travels through the conduits into low pressure accumulators where it can be collected in a rapid fashion. A pump is typically employed to remove the fluid from the accumulators and return it to the master cylinder.
Conventionally, ABS's have included pumps for draining such accumulators that run continuously throughout all three modes discussed above. Such continuous pump operation is unnecessary, and, at times, undesirable. The pump that drains the accumulators need only operate during the third mode when pressure is being decreased within the system.
Conventional continuous pump operation includes several limitations and drawbacks. First, the pumps typically generate noise at levels that can be disturbing and distracting to a vehicle operator. Second, continuous pump operation requires additional power consumption from a vehicle power source such as the main battery. Further, continuous pump operation potentially introduces excessive wear on the moving parts within the pump and, potentially, other components of the braking system.
Therefore, it is desirable to have cyclical pump operation such that the pump operates to drain the low pressure accumulators only at preselected intervals. This invention addresses the need for cyclical control of the accumulator draining pump and seeks to overcome the drawbacks and limitations discussed above. This invention provides a system for cyclically controlling pump activation during the pressure decrease mode of operation of an antilocking brake system.